Diaphragmatic surface of lung

The diaphragmatic surface (Base; Inferior surface) of the lung is the concave undersurface of each lung that rests upon and is molded to the convex dome of the diaphragm, which separates the thoracic cavity from the abdominal cavity. This surface is broader and more concave on the right lung than on the left, owing to the higher position of the right hemidiaphragm as it is pushed upward by the underlying right lobe of the liver.

Key anatomical features:

• The diaphragmatic surface is formed primarily by the lower lobes of both lungs, with a contribution from the middle lobe on the right side.

• It is covered by visceral pleura, which interfaces with the parietal (diaphragmatic) pleura lining the superior surface of the diaphragm, creating a potential pleural space lubricated by a thin layer of serous fluid to minimize friction during respiration.

• Posteriorly, the lung extends deep into the costophrenic (posterior diaphragmatic) sulcus. In living patients, lung tissue reaches at or below the level of the 12th rib in approximately 80% of individuals, and as low as the L1 vertebral body in 18% significantly lower than classical cadaveric teaching suggests.

• The right hemidiaphragm is molded over the convex surface of the right lobe of the liver, while the left hemidiaphragm is shaped by the left lobe of the liver, gastric fundus, spleen, and splenic flexure of the colon.

• Laterally and behind, the diaphragmatic surface is bounded by a thin, sharp margin which projects for some distance into the phrenicocostal sinus of the pleura, between the lower ribs and the costal attachment of the diaphragm.